Geometrical and electronic structures of tripotassium-doped hydrocarbon superconductors: Density functional calculations

TL;DR

This study uses density functional theory to explore the structures and electronic properties of potassium-doped polycyclic aromatic hydrocarbons, revealing complex Fermi surfaces and the role of potassium in superconductivity.

Contribution

It predicts the crystal configurations of several doped PAHs and analyzes their electronic structures, highlighting the impact of potassium hybridization on superconductivity.

Findings

Electronic structures are highly sensitive to molecular arrangements.

Potassium contributes to Fermi surfaces, especially K-3d electrons.

The rigid-band model is invalid due to hybridization effects.

Abstract

A systemically theoretical study has been presented to explored the crystal structures and electronic characteristics of polycyclic aromatic hydrocarbons (PAHs), such as solid phenanthrene, picene, 1,2;8,9-dibenzopentacene, and 7-phenacenes, since these PAHs exhibited the superconductivity when potassium doping into. For tripotassium-doped phenanthrene and picene, we demonstrate the K atomic positions to fit the experimental lattice parameters, and analyze the distinction between the stablest configuration and the fitted experimental one. Based on the first-principles calculations, for the first time, we predict the possible crystal configurations of pristine and tripotassium-doped 1,2;8,9-dibenzopentacene and 7-phenacenes, respectively. For these four PAHs, the electronic structures after doping are investigated in details. The results show that the electronic characters near the Fermi level are high sensitive to structure. Because of the change of the benzene rings arrangement, the 1,2;8,9-dibenzopentacene exhibits visibly different band structures from other three PAHs. In these metallic PAHs, two bands cross the Fermi level which results in the complicated multiband feature of Fermi surfaces. Fascinatingly, we find that the electronic states of potassium contribute to the Fermi surfaces especially for K-3$d$ electrons, which improves a way to understand this superconductivity. As a result, we suggest that the rigid-band picture is invalidated due to the hybridization between K atoms and PAH molecules as well as the rearrangement and distortion of PAH molecules.